In recent years, a material for an inductor or a transformer which is used in a power supply circuit such as DC-DC converter requires, small loss in high-frequency and large-amplitude excitation for obtaining high conversion efficiency, small remnant magnetic flux density for obtaining a predetermined amount of change of magnetic flux density even in applying a direct-current bias magnetic field thereto, and high resistivity for ensuring electric insulation with a conductor.
In particular, for improving reliability as parts, an inductor or a transformer is generally molded in a resin, and in a device of such a resin molding type, it is known that compression stress is applied to a core material in curing the resin.
That is, because a magnetic permeability and a core loss in the ferrite material used in the core material are changed according to magnitude of compression stress, an inductance value and loss of the device are changed before and after molding with the resin. Therefore, for obtaining more stable device performance, it is needful to use a ferrite material having small change of a magnetic permeability and a core loss with respect to compression stress.    [Patent Document 1] Japanese Patent Application Laid-Open No. 11-87126    [Patent Document 2] Japanese Patent Application Laid-Open No. 1-179402    [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-60224    [Patent Document 4] Japanese Patent Application Laid-Open No. 60-76107    [Patent Document 5] Japanese Patent Application Laid-Open No. 2000-269017    [Patent Document 6] Published Japanese Translation No. 9-505269 of the PCT Application